ProSoft Technology MVI71-MCM - Manual (Page 64)

MVI71-MCM ♦ PLC Platform Reference
Modbus Communication Module
Page 64 of 111 ProSoft Technology, Inc.
December 28, 2007
This sequence will continue until interrupted by other write block numbers sent by
the controller or by a command request from a node on the Modbus network or
operator control through the module's Configuration/Debug port.
If the ladder logic does not send a BTW instruction to the module quickly enough,
it is possible for the MVI71-MCM module to send a new BTR instruction
requesting the same write block ID.
Write Block
These blocks of data transfer information from the PLC processor to the module.
The structure of the output image used to transfer this data is shown in the
following table:
Offset Description Length
0 Write Block ID 1
1 to 60 Write Data 60
61 to 63 Spare 3
The Write Block ID is an index value used to determine the location in the
module's database where the data will be placed. Each transfer can move up to
60 words (block offsets 1 to 60) of data.
Status Data Block (Read Block ID = -1)
After the last Read Block is sent, the module builds a BTR block (ID = -1) to
transfer the module's status information to the processor. This information can be
used by the PLC program to determine the current status of the module. Ladder
logic should be constructed to transfer the information in this block to a user data
file. The structure of this block is shown in the following table:
Offset Content Description
0 Read Block ID Block identification code -1 to indicate a status block.
1 Write Block ID Block requested from the processor by the module.
2 Program Scan Count This value is incremented each time a complete program
cycle occurs in the module.
3 to 4 Product Code These two registers contain the product code of "MCM"
5 to 6 Product Version These two registers contain the product version for the
currently running software.
7 to 8 Operating System These two registers contain the month and year values for
the program operating system.
9 to 10 Run Number These two registers contain the Run Number value for the
currently running software.
11 Port 1 Command List
Requests This field contains the number of requests made from this
port to slave devices on the network.
12 Port 1 Command List
Response This field contains the number of slave response messages
received on the port.
13 Port 1 Command List
Errors This field contains the number of command errors processed
on the port. These errors could be due to a bad response or
command.
14 Port 1 Requests This field contains the total number of messages sent out of
the port.